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PES 112 General Physics II
Practice Exam 2
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Definitions & Concepts (2 pts each)
1. At what time is the current greatest in a circuit containing a discharging capacitor?
a. A long time after the capacitor first begins to discharge
b. One time constant after the capacitor first begins to discharge
c. Immediately after the capacitor begins to discharge
d. The current is constant at all times
2. The terminal voltage of a battery is always greater than or equal to the ideal voltage.
a. True
b. False
3. What units will result from dividing Coulombs by the product of Ohms times Farads?
a. Volts
b. Amps
c. Watts
d. Joules
Applications (4-6 pts each)
4. What is the equivalent capacitance of the combination shown?
12 μF
24 μF
20 μF
12 μF
5. An air-filled parallel plate capacitor is constructed with a capacitance of 6μF. If the plates are
0.1 mm apart, what is the area of one of the plates? A voltage source of 12 V is connected
across the capacitor. How much charge eventually moves onto the positive plate? How much
energy is now contained in the capacitor? How much energy is expended by the voltage
source in moving this charge? Some Pyrex glass (dielectric constant of 5.6) is inserted
between the plates and the capacitor is again connected to the same voltage source. How much
energy is now stored in the capacitor?
R. Gist
1 of 2
Long Semester Ver. B, Rev 1
PES 112 General Physics II
Practice Exam 2
6. A rod of 2.0-m length and a square (2.0 mm x 2.0 mm) cross section is made of a material with
–8
a resistivity of 6.0 x 10 Ω ⋅ m at 20o Celcius. What is the resistance of the rod at this
temperature? If a potential difference of 0.50 V is placed across the ends of the rod, what is the
initial current, and at what rate is heat (Joule heating) generated in the rod the instant current
begins to flow? The material then heats up to an operating temperature of 500 degrees Celcius.
The temperature coefficient of the material is 0.5 x 10-3 Kelvin-1. What are the operating
resistance and current of the material?
7. A certain battery has a rated voltage of 9 V and an internal resistance of 0.1-Ω. If the battery is
connected to a 10- Ω resistor, what is the terminal voltage of the battery?
10 Ω
8. What is the magnitude of the current in the 20-Ω resistor
shown?
+
+
20 Ω
10 V
15 V
−
−
10 Ω
9. If R = 20 Ω, what is the equivalent resistance between points
A and B in the figure?
R
2R
4R
R
2R
4R
A
B
10. A 10-mF capacitor is initially charged, then it is connected to a circuit containing a 100-W
resistor and allowed to discharge. How long does it take to reach 55% of its initial charge?
What is the current at this instant?
Constants
εo
R. Gist
Permittivity of free space
2 of 2
8.854 x 10-12
Long Semester Ver. B, Rev 1